Molar-incisor hypomineralisation is systemic caused malformation, which is presented as discolorations on tooth surface with clear boundaries. The malformation can be found on first permanent molars and sometimes also in combination with permanent incisors. In some cases, it may also be present on second deciduous molars. The color of discoloration depends on the depth of hypomineralisation of the enamel, and may vary from white creamy specks to yellow and brown. Diagnostic envelope of MIH contains: demarcated lesions on molars and incisors, post-eruptive breakdown of enamel, presence of atypical restorations and extractions due to MIH. Apart from aesthetic problems, the lesions might cause hypersensitivity to thermic and mechanic stimulations, susceptibility to post-eruptive breakdowns and caries. Due to chronic pulpitis, anesthesia often is not possible. The malformation is known to practitioners for more than 30 years, however, to this day its etiology is not yet established. The latest theory assumes MIH to be connected to multifactorial causes with genetical background. Prenatal, perinatal and postnatal medical complications until the fourth year of life are considered as a part of etiology. According to different studies, the prevalence across the world severely varies; its range is reported to be between 3% and 40% of population. Furthermore, MIH challenges practitioners; the hypomineralisation causes up to 10 times more frequent visits to dental offices, and complications caused by MIH represent additional problems regarding choice of restorative material and behavioural management. In order to assess the prevalence, several different classifications were introduced, the most recent, thorough and in use nowadays is EAPD classification from 2015